Mounted points



y 1951 F. 1.. CURTIS 2,984,555

MOUNTED POINTS Filed April 9, 1958 mv NTOR fTEl-I'D L. 02775 fatesMOUNTED POINTS Filed Apr. 9, 1958, Ser. No. 727,397

2 Claims. (Cl. 51-309) The invention relates to mounted points. Thisapplication is a continuation-in-part of my co-pending application Ser.No. 628,692, filed December 17, 1956, now abandoned.

One object of the invention is to provide a mounted point for grindingvery small bores. Another object of the invention is to provide agrinding wheel for the grinding, lapping, or finishing of small boresand small holes. Another object is to provide a grinding wheel of thetype indicated which is inexpensive to manufacture. Another object is toprovide a tiny grinding wheel of adequate strength.

Another object is to provide a grinding wheel of the character indicatedwhich holds its size very well. Another object is to provide a smallgrinding wheel which is satisfactorily eflicient in grinding. Anotherobject is to provide such a grinding wheel in the form of a mountedpoint which gives a good finish to the part ground.

Other objects will be in part obvious or in part pointed outhereinafter.

In the accompanying drawings illustrating my mounted point and themanufacture thereof,

Figure 1 is an elevation of a steel spindle.

Figure 2 is an elevation of the spindle of Figure 1 after the toolportion has been coated in accordance with this invention to produce thecompleted mounted point,

Figure 3 is an elevation on an enlarged scale of the mounted point ofFigure 2 showing the tool portion and its coating in section, and

Figure 4 is a photographic enlargement of a section through the tool endof a mounted point according to the invention.

The term mounted point has now for a long time designated a grindingwheel which can be but does not have to be cylindrical and which ismounted on one end of a spindle the shank of which can be clamped in achuck of a power hand tool such as an electric motor driven hand tool oran air motor driven hand tool. Such mounted points have also for a longtime now been used in internal grinding machines by clamping the shankof the spindle in a chuck which is part of the wheel head and is rotatedat high speed. These internal grinding machines are precision machinetools. The foregoing explains what I mean by mounted points.

Referring now to Figures 1, 2 and 3, the mounted point comprises a metalspindle 11 having illustratively a straight shank portion 12 with arounded end 13 for convenient mounting in the chuck of a wheel head orof a power hand tool and, integral therewith, a tapered portion 14,connecting the straight part of the shank 12 to a tool portion 15 and,as a matter of choice, there may be an intervening portion such as theportion 16 herein shown in Figures 1, 2 and 3 as straight, that iscylindrical.

In an illustrative embodiment of the invention as shown in Figures 1, 2and 3 the tool portion 15 consists of an originally cylindrical butknurled head 17 and a reduced diameter straight cylindrical portion 18.All these iQQ details can be widely varied so long as the spindle has ashank portion and a tool portion. All portions of the spindle should berigid with each other and ease of manufacture dictates integrality ofstructure but interfitting of the shank 11 and the tool portion 17 isnot precluded provided a rigid spindle results. Other metals can beused, the requirement of strength and rigidity making steel thepreferred metal and the requirement of rigidity as well as thedesirability that the spindles shall not readily rust makes thestainless steels preferred. These are nationally identified by numbersand I now prefer No. 410 stainless steel which has been and for sometime on a large scale used for mounted point spindles.

Whether or not the tool portion 15 includes a portion 18 of reduceddiameter is a matter of choice, although it will be seen that a veryfine interlock is provided thereby. It is highly desirable, however, tohave, as part of the tool portion 15, a knurled head 17. Conventionalknurling consists of crisscross threads producing pyramidal elevationsand this is highly satisfactory. The knurling operation swages some ofthe metal outwardly and this is the reason for the reduced diameterportion 18 since the knurling was done on the outer part of the toolportion '15, but it results in the aforesaid advantageous feature.Equally well, however, the entire tool portion 15 might be knurled.While conventional knurling is highly satisfactory any other substantialdeformation of the tool portion as by cutting, stamping, pressing mightbe adopted.

Ialso find it advantageous to blast the tool portion 15. This makes aroughened surface with which the coating 21 hereinafter described caninterlock microscopically as it interlocks macroscopically with theknurls. A macroscopically roughened surface is one in which theindividual elevations and depressions can be seen with the naked eye. Amicroscopically roughened surface is one in which they cannot be soseen. Surface blasting produces a surface of the latter kind. As anexample of surface blasting I have used with satisfaction No. 25 steelshot ejected from a blast nozzle with compressed air, a process now wellknown. Another material for blasting which would be very satisfactory issilicon carbide for example of No. 16 grit size, although finer gritsizes could be used and in some cases coarser grit sizes would besatisfactory. A surface having been roughened in this manner will bereferred to as a blasted surface.

To the tool portion 15 I now apply a coating of fused abrasive materialthe major portion by weight of which is fused crystalline metal oxidehaving a sharp melting point, said metal oxide being metal oxideselected from the group consisting of aluminum oxide, zirconium oxide,titanium oxide and mixtures thereof, which abrasive material is flamesprayed in situ on the tool portion. This coating may be applied inaccordance with U.S. Patent No. 2,707,691 granted May 3, 1955, onapplication of my colleague W. M. Wheildon, Jr. which describes a flamespraying gun for the purpose. Complete information for producing acoating as above defined is set forth in the Wheildon patent. Thematerial is supplied to the gun in the form of rods. These flamespraying guns are on the market and can be procured, for example, fromMetallizing Co. of America, Chicago 24, Illinois.

I prefer to use aluminum oxide, A1 0 as the material for the coating 21.Fused zirconia has recently been found to be an effective abrasivematerial, see U.S. Patent No. 2,769,699 granted on application of mycolleague F. J. Polch on November 6, 1956. This also may be used. Fusedzirconia-titania has also been found to be an effective abrasivematerial, see US. Patent No. 2,653,107 granted on application of W. B.Blumenthal on September 22, 1953. Therefore it is certain that fusedtitanium oxide also can be used. These three oxides mina base, titaniabase, and zirconia base powders.

point and it also is fused in the gun.

lwhich was only of slightly larger diameter. a mounted point could notbe made with a diameter less .sive material, as it has been fused in thegun.

3 are compatible in fact regular grade fused aluminum oxide containsquite a good proportion of titanium oxide. Therefore mixtures of thethree or of any two in any proportion can be used.

The rods can be entirely of crystalline metal oxide and thus can besintered rods of only the oxide or mixtures in question, without anysubstantial amount of lower melting point material as bond, such asfired clay or glass. On the other hand in order to produce a freecutting wheel, for the portion 21 is a grinding wheel and may havesubstantial depth as shown, a considerable proportion of clay or glassybond may be included in the rod resulting in a wheel 21 which has someof the characteristics of vitrified bonded fused alumina Wheels. Aluminais synonymous with aluminum oxide, zirconia with zirconium oxide andtitania with titanium oxide.

Instead of using a rod spraying gun I may use a powder spraying gun,such as a Metco Thermo Spray Gun manufactured and sold by MetallizingEngineering Company,

Inc., Westbury, Long Island, New York. I am not aware of any patent socannot cite one. This gun sprays ceramic powders of many differentkinds, including alu- For many grinding operations a large portion ofsilicate materials is desirable in the abrasive coating to make it freecutting by erosion of the silicate material, and any abrasivecomposition which has been found to be useful in the vitrified abrasiveart can be applied as a coating with one or the other of the flamespraying guns herein identified. This silicate material can be any ofkaolin, ball clay, mixtures of these, glassy frits of any kind andmixtures too, and with the kaolin or ball clay or both and with orwithout the addition of feldspar, which is a flux or flint which is ahardener. The coating is fused abrasive material which means that it hasbeen fused.

'Silicates dont have any sharp melting point, but in the guns they arefused to a free flowing condition.

The pure metal oxide material has a sharp melting At least a majorportion by weight of the metal oxide component must function as anabrasive, and the test of this is does it have a sharp melting point.Having a major portion by weight of such metal oxide as defined hereinthe coating is abrasive and can cut metals including hard steels if theharder metal oxides are used such as those mentioned.

In most cases aluminum oxide will be preferred except for the grindingof titanium and zirconium and similar "metals where zirconium oxide maybe preferred, or

titanium oxide or mixtures.

A mounted point according to this invention the abrasive of which wassubstantially pure fused alumina, and

which was sixty-five one-thousandths of an inch (65 mils) in diameterwas used to grind a hole in a piece of steel Heretofore than about onehundred one-thousandths of an inch (100 mils). This mounted point wasrotated at the high rate of 100,000 r.p.m. This job simply could not bedone at all prior to my invention. The grinding rate was quitesatisfactory and in a job such as this, a wide variation in grindingtime is of little consequence, as the grinding operation only takes afew seconds and setting up time takes a matter of several minutes. And asimple calculation shows that the grinding was done at a surface speedof 1,700 surface feet per minute, which is very slow (6,500 is normal)and a material which will grind at all at this speed had to be a verygood abrasive material.

powder.

As explained in the Wheildon patent aluminum Oxide when it becomes thecoating 21, is gamma type aluminum oxide. This has not heretofore beenknown as having high abrasive properties but I have found that it does.The abrasive of the mounted point of Figure 4 is gamma type aluminumoxide without any silicate bonding material. As can be seen from Figure4 it is dense and would hardly be considered to be a good abrasivematerial because a good abrasive material was supposed to be necessarilyporous. It has heretofore been considered that a monophase non porousmaterial could not be a good abrasive. According to the Wheildon patentthe porosity of flame sprayed pure alumina is from 8% to 11% open poresand up to 1% closed pores. This has been considered insufficient for agood abrasive material and therefore it is surprising that the mountedpoint of this invention should be a good abrasive material. The mountedpoint which was used in the grinding operation above described was thesame as that shown in Figure 4 only smaller. The mounted point of Figure4 and any made in accordance with the invention has all of theadvantageous features mentioned in the objects.

Zirconia as commercially available always contains a minor proportion ofhafnia and obviously I use the commercially available material. I haveused zirconia stabilized with about 5% of lime. This material, wascrystallographically, partly monoclinic and partly cubic, butsurprisingly the coatings were found to be cubic.

The advantage of stabilized zirconia is that it can be claims it isstated that the abrasive material is entirely fused crystalline cubiczirconium oxide, this material is included and the phrase includes thenormal variety having a minor portion of hafnia.

Titania (titanium oxide) has been used for flame spraying according tothe Wheildon patent. X-ray examination of the titania rods used showedonly the crystalline phase rutile. X-ray examination of the coatingproduced by flame spraying these rutile rods showed three broad lineswhich identified the material as a hitherto unknown form of titania.This has been christened by the scientists of the manufacturer of rodsfor flame spraying as gamma titania (gamma titanium oxide). It is nearlyamorphous as shown by the broadness of the X-ray lines. It is a goodabrasive material, especially when a fine finish is wanted. It is quitecompatible with gamma alumina and with cubic zirconia as they are Witheach other. So also are alpha alumina, monoclinic zirconia and rutile inthe rods. It is within the scope of this invention to provide grindingwheels bonded with vitrified bonding material, or with organic bondingmaterial or metallic bond in which the abrasive is gamma alumina orgamma titania, neither ever having been used as abrasive material priorto my invention, and also in such wheels to provide abrasive made out ofa mixture of the oxides of aluminum, zirconium and titanium whichmixture was 'never used as an abrasive material before my invention.

V =Gr (centrifugal force equation) V=velocity in feet per second=1700/60G=centrifugal force in feet per second at periphery r=radius of body infeet Constant of gravity to convert to gravitational units,

Then G=V r in feet per second G= V /32r in gravitational unitsG=1700/60X1700/60 1/32 X 12/.0325 G=9,260 in gravitational units g Butthis G is the centrifugal force unit in terms of the gravitational unitat the periphery and at the center of the wheel it is zero, so the truemultiplier becomes half of the above value which is 4,630.

In calculating tangential stress a diametral band of the material ofunit width is taken, of length the same as the diameter, of thicknessthe same as the radius. The specific gravity of the abrasive materialwas believed to be 3, and the weight of a cubic inch of water is .036pound. A cubic inch of this material weighs .108 pound.

But the width of the material (unit) and the thickness of the materialcancel out since pounds per square inch tangential stress T is wanted,so the equation becomes:

T=specific gravity 3 water factor .036 length .065

Xmultiplier T=pounds per square inch tangential compressive stress Thisis the result that is a little high and the true figure is substantiallybelow 32 pounds per square inch.

The tensile strength of the all aluminum oxide coating has been testedand found to be 800 pounds per square inch. The factor of safety wastherefore, in this particular wheel, over 25' to 1 at the speed of100,000 rpm. Obviously much larger mounted points can be made andoperated at even higher speeds. The limiting factor will be the grindingstresses rather than the centrifugal force.

It will thus be seen that there has been provided by this inventionmounted points in which the various objects hereinabove set forthtogether with many thoroughly practical advantages are successfullyachieved. As many possible embodiments may be made of the aboveinventiofi'and as many changes might be made in the embodiment above setforth, it is to be understood that all matter hereinbefore set forth isto be interpreted as illustrative and not in a limiting sense.

I claim:

1. A small sized mounted point comprising a spindle having a shankportion and a roughened tool portion, a homogeneous abrasive grindingtip portion integral with said tool portion, said grinding tip portionforming the sole grinding element of the tool portion. and consisting ofa flame sprayed coating deposited in situ on said tool portion andforming the entire grinding surface thereof, and said grinding tiphaving as an abrasive therein a major proportion of fused crystallinegamma aluminum oxide.

2. A small sized mounted point comprising a spindle having a shankportion and a roughened tool portion, a homogeneous abrasive grindingtip portion integral with said tool portion, said grinding tip portionforming the sole grinding element of the tool portion and consisting ofa flame sprayed coating deposited in situ on said tool portion andforming the entire grinding surface thereof, and said grinding tip beingformed of an abrasive fused crystalline gamma aluminum oxide.

References Cited in the file of this patent UNITED STATES PATENTS1,528,639 Tone Mar. 3, 1925 2,286,292 Mall June 16, 1942 2,366,767Brooks Jan. 9, 1945 2,428,823 Wright Oct. 14, 1947 2,535,526 Ballard eta1. Dec. 26, 1950 2,562,587 Swearingen July 31, 1951 2,653,107Blumenthal Sept. 22, 1953 2,707,691 Wheildon May 3, 1955 2,769,699 PolchNov. 6, 1956 2,877,105 Smith Mar. 10, 1959

1. A SMALL SIZED MOUNTED POINT COMPRISING A SPINDLE HAVING A SHANKPORTION AND A ROUGHENED TOOL PORTION, A HOMOGENEOUS ABRASIVE GRINDINGTIP PORTION INTEGRAL WITH SAID TOOL PORTION, SAID GRINDING TIP PORTIONFORMING THE SOLE GRINDING ELEMENT OF THE TOOL PORTION AND CONSISTING OFA FLAME SPRAYED COATING DEPOSITED IN SITU ON SAID TOOL PORTION ANDFORMING THE ENTIRE GRINDING SURFACE THEREOF, AND SAID GRINDING TIPHAVING AS AN ABRASIVE THEREIN A MAJOR PROPORTION OF FUSED CRYSTALLINEGAMMA ALUMINUM OXIDE.